KR102542595B1 - METHOD AND APPARATUS OF HAND OVER IN WIRELESS COMMUNICATION SYSTEM SUPPORTING FUNCTION OF CELL RANGE SUPPORTING eICIC - Google Patents

Abstract

The present invention relates to a handover method and apparatus in a wireless communication system supporting an eICIC function, and a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function. In the communication method of the first base station, monitoring whether the cell extension function is deactivated, generating a handover request message when the deactivation of the cell extension function is detected, and sending the handover request message as the It may include transmitting to a second base station.

Description

Handover method and apparatus in wireless communication system supporting eICIC function

The present invention relates to a handover method and apparatus in a wireless communication system supporting an eICIC function, and more particularly, to a method and apparatus for handing over a terminal according to whether a cell extension area function is activated in a wireless communication system.

In general, mobile communication systems have been developed to provide voice services while ensuring user activity. However, mobile communication systems are gradually expanding their range to data services as well as voice, and have now developed to the extent that they can provide high-speed data services. However, in the mobile communication system currently providing services, a more advanced mobile communication system is required due to a shortage of resources and users' demand for higher-speed services.

In response to this demand, as one of the systems under development as a next-generation mobile communication system, the 3rd Generation Partnership Project (3GPP) is working on the standardization of Long Term Evolution (LTE). LTE is a technology for realizing high-speed packet-based communication with a transmission rate of up to hundreds of Mbps. To this end, various methods are being discussed. For example, a method of reducing the number of nodes located on a communication path by simplifying a network structure or a method of bringing wireless protocols closer to a wireless channel as much as possible.

In particular, recently, standardization for time-domain inter-cell interference coordination (Time-Domain Inter-Cell Interference Coordination) has been progressed, and accordingly, the need for the base station to effectively manage the terminal has emerged.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method and apparatus for a base station to efficiently manage a terminal in a heterogeneous network mobile communication system in which a macro cell and a small cell are mixed.

More specifically, the present invention is a heterogeneous network (HetNet) system in which a base station (macro cell) with high power and a base station (small cell) with low power share the same frequency and coexist. Its object is to provide a method and apparatus for preventing RLF (Radio Link Failure) from occurring.

The present invention provides a step of monitoring whether a cell range expansion function is deactivated in a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function, the cell extension region When function inactivation is detected, a communication method of a first base station including generating a handover request message and transmitting the handover request message to the second base station is provided.

The present invention may further include maintaining an almost blank subframe (ABS) function activation state of the first base station for a predetermined time when the deactivation of the cell expansion area function is detected.

The predetermined time is characterized in that the maximum time required for the second base station to hand over the terminal to the first base station.

Due to the inactivation of the cell extension function, the cell area of the second base station is changed from the first area to the second area, and the handover request message is located outside the second area and inside the first area. and is a message requesting handover of a terminal connected to the second base station to the first base station.

The present invention may further include receiving a handover complete message from the second base station and disabling an almost blank subframe (ABS) function of the first base station.

The first base station is a macro base station, and the second base station is a pico base station.

In a heterogeneous network wireless communication system including a first base station and a second base station supporting a Cell Range Expansion (CRE) function, the present invention provides a handover request message generated by deactivation of the cell extension region as described above. A handover method for a second base station is provided, which includes receiving from a first base station and handing over at least one terminal determined based on the handover request message to the first base station.

Due to the inactivation of the cell extension function, the cell area of the second base station is changed from the first area to the second area, and the handover step is located inside the first area and outside the second area. The method may include determining a terminal located and connected to the second base station and handing over the determined terminal to the first base station.

The present invention may further include generating a handover complete message after completing the handover of the terminal and transmitting the handover complete message to the first base station.

The first base station is a macro base station, and the second base station is a pico base station.

In a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function, the present invention monitors whether or not the cell range expansion function is deactivated, and the cell extension area A first base station including a first base station control unit generating a handover request message and a first base station transmitting/receiving unit transmitting the handover request message to the second base station when function inactivation is detected.

The controller of the first base station may maintain an almost blank subframe (ABS) function activation state of the first base station for a predetermined time when deactivation of the cell expansion area function is detected.

The predetermined time is characterized in that the maximum time required for the second base station to hand over the terminal to the first base station.

Due to the inactivation of the cell extension function, the cell area of the second base station is changed from the first area to the second area, and the handover request message is located outside the second area and inside the first area. and is a message requesting handover of a terminal connected to the second base station to the first base station.

The transceiver of the first base station receives a handover complete message from the second base station, and when the handover complete message is received through the transceiver, the controller of the first base station receives an almost blank subframe (ABS) of the first base station. It is characterized by inactivating the function.

The first base station is a macro base station, and the second base station is a pico base station.

In a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function, the present invention provides a handover request message generated by deactivation of the cell extension region. A second base station including a second base station transceiver received from the first base station and a second base station controller for handing over at least one terminal determined based on the handover request message to the first base station.

Due to the inactivation of the cell extension function, the cell area of the second base station is changed from the first area to the second area, and the second base station controller is located inside the first area and outside the second area. and determining a terminal connected to the second base station, and handing over the determined terminal to the first base station.

The control unit of the second base station generates a handover complete message after completion of the handover of the terminal, and the transceiver of the second base station transmits the handover complete message to the first base station.

The first base station is a macro base station, and the second base station is a pico base station.

According to the present invention, in a heterogeneous network mobile communication system in which a macro base station and a small base station are mixed, occurrence of RLF (Radio Link Failure) due to inactivation of a Cell Range Expansion (CRE) function can be prevented.

1 is a diagram illustrating that coverage of a small cell is extended when eICIC technology is used.
2 is a diagram illustrating a cell area management method according to an embodiment of the present invention.
3 is a diagram illustrating an area in which an eICIC terminal can be located for each group according to an embodiment of the present invention.
4A is a diagram illustrating communication between a base station and a terminal when a cell extension function is activated.
4B is a diagram illustrating communication between a base station and a terminal when a cell extension function is deactivated.
5 is a diagram illustrating a communication method of a first base station according to an embodiment of the present invention.
6 is a diagram illustrating a communication method of a first base station according to an embodiment of the present invention.
7 is a diagram illustrating a handover method of a second base station according to an embodiment of the present invention.
8 is a diagram illustrating a handover method in a wireless communication system supporting an eICIC function according to an embodiment of the present invention.
9 is a block diagram illustrating the internal structure of a first base station according to an embodiment of the present invention.
10 is a block diagram illustrating an internal structure of a second base station according to an embodiment of the present invention.

In describing the embodiments, descriptions of technical contents that are well known in the technical field to which the present invention pertains and are not directly related to the present invention will be omitted. This is to more clearly convey the gist of the present invention without obscuring it by omitting unnecessary description.

For the same reason, in the accompanying drawings, some components are exaggerated, omitted, or schematically illustrated. Also, the size of each component does not entirely reflect the actual size. In each figure, the same reference number is assigned to the same or corresponding component.

Advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the present embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

At this time, it will be understood that each block of the process flow chart diagrams and combinations of the flow chart diagrams can be performed by computer program instructions. These computer program instructions may be embodied in a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, so that the instructions executed by the processor of the computer or other programmable data processing equipment are described in the flowchart block(s). It creates means to perform functions. These computer program instructions may also be stored in a computer usable or computer readable memory that can be directed to a computer or other programmable data processing equipment to implement functionality in a particular way, such that the computer usable or computer readable memory The instructions stored in are also capable of producing an article of manufacture containing instruction means that perform the functions described in the flowchart block(s). The computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operational steps are performed on the computer or other programmable data processing equipment to create a computer-executed process to generate computer or other programmable data processing equipment. Instructions for performing processing equipment may also provide steps for performing the functions described in the flowchart block(s).

Additionally, each block may represent a module, segment, or portion of code that includes one or more executable instructions for executing specified logical function(s). It should also be noted that in some alternative implementations it is possible for the functions mentioned in the blocks to occur out of order. For example, two blocks shown in succession may in fact be executed substantially concurrently, or the blocks may sometimes be executed in reverse order depending on their function.

At this time, the term '~unit' used in this embodiment means software or a hardware component such as FPGA or ASIC, and '~unit' performs certain roles. However, '~ part' is not limited to software or hardware. '~bu' may be configured to be in an addressable storage medium and may be configured to reproduce one or more processors. Therefore, as an example, '~unit' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Functions provided within components and '~units' may be combined into smaller numbers of components and '~units' or further separated into additional components and '~units'. In addition, components and '~units' may be implemented to play one or more CPUs in a device or a secure multimedia card. Also, in an embodiment, '~ unit' may include one or more processors.

Hereinafter, in a heterogeneous network (HetNet) system in which a base station (macro cell) with high output and a base station (small cell) with low output share the same frequency, the cell range expansion (CRE) function A method and apparatus for handing over a terminal according to activation or not.

More specifically, an object of the present invention is to provide a method and apparatus for preventing RLF (Radio Link Failure) from occurring due to a cell area change of a base station in a heterogeneous network system.

In general, a macro cell has a wide area coverage with a relatively high output. On the other hand, a small cell has a relatively low output and a narrow area coverage compared to the coverage of the macro cell, but has the advantage of being able to expand the cell inexpensively.

The small cell is mainly used to fill a coverage hole area not covered by the macro cell or to absorb the load of the macro cell. However, since the small cell has a narrow coverage, there is a problem in that it cannot effectively absorb the load of the macro cell.

The 3GPP LTE standard introduces eICIC (enhanced Inter-Cell Interference Coordination, or time-domain ICIC) technology so that a small cell can effectively absorb the load of a macro cell.

In a cellular wireless communication system, it is common to designate a cell with the highest level of downlink received power for a given user as a serving cell, and operate the user to download data traffic from the serving cell. am. On the other hand, eICIC technology can designate a small cell as a serving cell and download data traffic from the small cell for a user whose downlink reception power of a macro cell is greater than that of a small cell. It is a standard technology that can make it possible.

1 is a diagram illustrating that coverage of a small cell is extended when eICIC technology is used.

As shown in FIG. 1 , when the eICIC technology is used, the second area 110, which is a conventional small cell coverage, may be extended to the first area 120. As a result, the small cell can absorb more users of the macro cell and distribute the load of the macro cell to the small cell.

On the other hand, as shown in FIG. 1, users located inside the extended small cell coverage, that is, inside the first area 120 and outside the second area 110, experience larger interference from the macro cell than the signal of the small cell. As a result, the radio channel quality may be greatly deteriorated. Accordingly, initiators located in the coverage of the expanded small cell may have difficulty in performing normal wireless communication.

To solve such a technical problem, 3GPP LTE eICIC technology provides ABS pattern technology and resource restriction technology.

According to the ABS pattern technology, a macro cell provides information called an ABS pattern to a small cell that suffers major interference from a corresponding cell. According to the eICIC standard of 3GPP LTE FDD, ABS pattern information is composed of a 40-bit bit stream, and means whether or not Tx Power of a macro cell that is repeated every 40 ms is restricted. For example, the value of the first bit among 40 bits may indicate whether or not Tx Power of the macro cell is restricted in the first subframe of the 40 ms period. For example, if the corresponding value is 1 (=ABS), it means that the macro cell reduces transmit power (Tx power), and if the corresponding value is 0 (= nonABS), it means that the macro cell is special transmit power (Tx power). ) can mean that it is not constrained.

According to the eICIC technology, since a UE located in the extended coverage of a small cell experiences high interference from a macro cell, radio resources are allocated only to the ABS that reduces Tx power in the macro cell for the radio channel. It is advantageous to ensure quality.

That is, the ABS pattern is a technology that allows users located in an extended coverage of the small cell to stably perform wireless communication by explicitly notifying the small cell of whether or not the Tx power of the macro cell is reduced.

Meanwhile, a resource restriction technique is a technique for inducing a user to measure a channel only in a specific subframe.

There may be three patterns in the resource limitation technique.

The first pattern consists of 40 bit information, and serves to restrict the subframe in which the user measures RSRP and RSRQ for the serving cell and determines Radio Link Failure (RLC).

The second pattern is composed of 40-bit information and serves to restrict subframes for measuring RSRP and RSRQ for a neighbor cell by a user.

The third pattern consists of two pieces of 40-bit information. The first 40 bits may serve to inform a subframe to be used for measuring the first channel quality (CQI: Channel Quality Indicator). The second 40 bits serve to inform the subframe to be used for measuring the second channel quality.

According to the general eICIC technology, the network may allow a user to measure channel quality in ABS and channel quality in non-ABS by using a third pattern. Using this, when allocating radio resources to users, the network may perform resource allocation and modulation and coding scheme (MCS) determination by applying an appropriate channel quality according to ABS of a corresponding subframe.

For reference, while the ABS pattern may change over time, it is necessary to efficiently operate the third pattern in consideration that transmitting the third pattern to the user causes signaling overhead.

Meanwhile, the 3GPP LTE standard also introduced FeICIC (Further enhanced Inter-Cell Interference Coordination) technology to provide a more effective load balancing function.

In the FeICIC technology, a base station transmits interfering cell information to a terminal through signaling, thereby removing interference caused by a cell-specific reference signal (CRS) generated from an interfering cell to improve channel quality. made it possible

In particular, when the macro cell performs ABS, since the channel quality of the small cell UE can be improved, FeICIC is expected to provide an effect of expanding the coverage of the small cell more widely than the existing eICIC.

An object of the present invention is to provide a method and apparatus for a base station to effectively manage a terminal in a heterogeneous network mobile communication system in which a macro cell and a small cell are mixed. This specification is described based on the 3GPP LTE FDD wireless communication system standard, but it can be extended to other communication systems, of course. In addition, this specification is described as a criterion for extending the coverage of a small cell in a network in which macro cells and small cells coexist, but it can be extended to other types of cell configurations as well. Although this specification intends to describe a pico cell as an example of a small cell for convenience, it is not necessarily limited thereto, and remote radio equipment (Remote Radio Head, RRH), transmission point (Transmission Point, TP), etc. An embodiment of the present invention can also be applied to the node of the same principle.

2 is a diagram illustrating a cell area management method according to an embodiment of the present invention.

Hereinafter, the 'cell area 120 after cell area expansion' compared to the 'cell area 110 before cell area expansion' of the pico cell is referred to as a cell expansion area (CRE area).

In this case, it should be noted that according to an embodiment of the present invention, the 'cell area 120 after cell area expansion' may be used as a meaning not including the 'cell area 110 before cell area expansion'.

A terminal located in an area where cell expansion of a pico cell is possible and using a macro cell as a serving cell is referred to as a 'macro CRE terminal' 210 .

Among the terminals using the macro cell as a serving cell, terminals excluding the 'macro-CRE terminal' are referred to as 'macro non-CRE terminal' 220 .

A terminal located in the cell extension area of the pico cell and using the pico cell as a serving cell is referred to as a 'pico CRE terminal' 230 .

Among the terminals using the pico cell as a serving cell, terminals excluding the 'pico CRE terminal' are referred to as 'pico non-CRE terminals' 240 .

In the cell area management method shown in FIG. 2 , the coverage expandable area (reserve area or CRE area) in the pico cell is designated as a 'shared cell area' of the macro cell and the pico cell, rather than the specific cell area of the macro cell or pico cell. characterized by operation.

In an embodiment of the present invention shown in FIG. 2, UEs belonging to a reserved area are distinguished through a unique UE management method. The macro cell distinguishes between a macro UE (macro CRE UE) in the CRE area and a macro UE (macro non-CRE UE) not located in the CRE area.

Likewise, the pico cell distinguishes between a pico CRE UE within the CRE area and a pico non-CRE UE not located within the CRE area.

According to an embodiment of the present invention shown in FIG. 2, when the load difference between the macro cell and the pico cell becomes larger than a predetermined threshold, a CRE area UE having a cell with a high load as a serving cell is assigned to a cell with a low load. You can force handover.

On the other hand, since the cellular system applies hysteresis to handover occurrence conditions in order to prevent a handover pingpong phenomenon, a shared cell area is generally formed.

For example, a shared cell area formed at the boundary between a macro cell and a pico cell is an area that is either a macro cell area or a pico cell area, and handover does not occur when a UE moves within the corresponding area. A shared cell area is a good way to prevent handover pingpong, but has a disadvantage in that the UE does not have an optimal cell in terms of signal strength as a serving cell. For example, a pico UE may be located where a larger macro cell signal is received than a macro UE.

Since the embodiment according to the drawing shown in FIG. 2 uses a method of operating a wider shared cell area (or CRE area) existing on the boundary between the macro cell and the pico cell, the UE serves the optimal cell in terms of signal strength. There is a possibility that it cannot be obtained as a cell.

3 is a diagram illustrating an area in which a UE can be located for each group in a wireless communication system supporting the eICIC function of the present invention.

The group refers to four groups of macro non-CRE UEs, macro CRE UEs, pico non-CRE UEs, and pico CRE UEs. Since the definition of each group has been described in FIG. 2, a detailed description thereof will be omitted.

An area where the area where the macro CRE UE is located and the area where the pico CRE UE is located overlap each other corresponds to the CRE area.

Specifically, when the macro UE passes eICIC_B, it is managed as a macro CRE UE. However, it has not yet been handed over to the pico cell. However, when the macro UE passes through the extended CIO, that is, eICICCIO, the macro CRE UE can be handed over to the picocell.

Unlike FIG. 3, if eICICCIO is extended to eICIC_B, the macro UE can be directly handed over to the picocell when eICIC_B is passed. That is, from the point of view of the macro UE, it is managed as a macro cell UE within the expandable area of the pico cell, but can be managed as a pico cell UE when entering the pico cell extension area.

Unlike this, when the pico UE passes the pre-expansion cell boundary (MROCIO), it is managed as a pico CRE UE until it passes the eICICCIO, and then it can be handed over to the macro cell after passing the eICICCIO. If eICICCIO is determined up to eICIC_B, the pico UE can continue to be managed as a pico CRE UE until eICIC_B passes.

Referring to FIG. 3 , for example, as in the case of the illustrated UE, the macro UE 300 may be located in a place where a larger pico cell signal is received than the pico UE 310, but unnecessary radio waves due to degraded radio channel quality. It may be desirable to exchange the serving cells of the two UEs as this results in a waste of resources.

On the other hand, according to an embodiment of the present invention, the A3 event of the 3GPP LTE standard is applied to classify CRE area UEs. When the entry condition is satisfied, the MR is operated to be transmitted only once.

However, since the same A3 event is used for HO determination for other cells, transmitting the MR only once may cause deterioration in HO quality.

4A is a diagram illustrating communication between a base station and a terminal when a cell extension function is activated.

As described above, when the cell extension area function, that is, the CRE function is activated, the cell coverage of the pico base station 420 is extended from the second area 450 to the first area 460. Also, the ABS function is activated so that the macro base station 410 can form an ABS pattern as shown in FIG. 4A.

In this case, the terminal 440 located inside the second region 450 communicates with the pico base station 420 regardless of whether the cell extension region function is activated or deactivated.

On the other hand, the terminal 430 located outside the second area 450 and inside the first area 460 communicates with the macro base station 410 before the cell extension area function is activated. And, after the cell extension function is activated, communication with the pico base station 420 is performed.

More specifically, the macro terminal 430 connected to the macro base station 410 belonging to the cell expansion area of the pico base station 420 is configured to form the ABS pattern of the macro base station 410 to the cell of the pico base station 420. When entering the extended area, the macro terminal 430 may be handed over from the macro base station 410 to the pico base station 420 .

That is, when the cell extension function is activated, the macro base station 410 activates the ABS pattern function as shown in FIG. 4A, and the pico base station 420 uses the ABS pattern to generate interference from the macro base station 410. Communication with the terminal 430 may be performed without

4B is a diagram illustrating communication between a base station and a terminal when a cell extension function is deactivated.

When the cell extension function is changed from an active state to an inactive state, the cell coverage by the pico base station 420 is changed from the first region 460 to the second region 450 .

In this case, the terminal 440 located inside the second area 450 maintains communication with the pico base station 420 because it is still within the cell coverage of the pico base station 420 even if the cell extension function is changed to an inactive state. can

On the other hand, as the cell extension area function of the terminal 430 located outside the second area 450 and located inside the first area 460 is changed to an inactive state, as shown in FIG. 4B, RLF (Radio Link Failure) may occur.

That is, when the cell extension function is deactivated, RLF may occur in a pico CRE UE located in the cell extension region among UEs capable of supporting ABS. In the macro CRE UE located in , even if the cell extension function is disabled, RLF does not occur.)

More specifically, the RLF generated in the terminal 430 is deactivated due to cell extension region deactivation and the ABS function of the macro base station 410 is also deactivated, so interference of the macro base station 410 is caused by the pico base station 420 and the terminal ( 430) can occur by affecting communication between them.

Therefore, in order to prevent the occurrence of the RLF, even if the cell extension area function is deactivated, the ABS function is kept active before the terminal 430 is handed over to the macro base station 410 to prevent interference by the macro base station 410. need to be minimized.

Therefore, the present invention intends to disclose a method for preventing RLF generation due to cell extension function inactivation by maintaining the ABS function activation state of a macro base station for a certain period of time even if the cell extension function is deactivated, and a detailed description thereof is provided. 5 will be explained later.

5 is a diagram illustrating a communication method of a first base station according to an embodiment of the present invention.

In step S510, the first base station monitors whether the cell extension area function is deactivated. As described above, since the occurrence of RLF in the terminal is highly likely to occur at the moment when the cell extension function is converted from an active state to an inactive state, the first base station can monitor in real time whether or not the cell extension function is deactivated. can

Here, the first base station may mean a macro base station, and the first base station monitors whether the cell extension function is deactivated at a predetermined periodic interval in addition to monitoring whether the cell extension function is deactivated in real time. load can be reduced.

If it is determined through step S520 that the cell extension function is still active, the first base station returns to step S510 and continuously monitors the cell extension function state.

On the other hand, when deactivation of the cell extension function is detected, the first base station maintains the ABS function activation state through step S530. Here, the cell extension area function may be deactivated for various reasons. For example, if the load of the first base station increases, it is inefficient to keep the ABS function activated. In this case, the first base station may deactivate the cell extension area function.

Previously, it was disclosed that when the cell extension area function is deactivated, the ABS function of the first base station is also deactivated and RLF may occur in a terminal located in a specific area. To prevent such RLF from occurring, the first base station in step S530 Even if the cell extension area function is deactivated, the ABS function remains active.

In step S540, the first base station generates a handover request message. The handover request message refers to a message for handing over a terminal in which RLF may occur due to inactivation of a cell extension area function to a first base station.

Specifically, when the cell extension area function is deactivated, the cell area of the second base station corresponding to the pico base station may be changed from the first area to the second area. In this case, before handing over of a terminal located outside the second area and inside the first area and connected to the second base station to the first base station, RLF receives interference from the first base station. can happen

Therefore, the first base station is located in the area (the area outside the second area and inside the first area) through step S540 and generates a message for handover of the terminal connected to the second base station. Here, the UE may be a pico CRE UE, which means a UE located in a cell extension area of a pico cell and using the pico cell as a serving cell as described above.

In step S550, the first base station transmits the handover request message generated in step S540 to the second base station. As described above, the second base station is a base station whose cell area is changed due to inactivation of the cell extension area function, and may be a pico base station.

The handover request message may be transmitted from the first base station to the second base station with a separate step only for transmitting the handover request message, or from the first base station to the second base station due to the inactivation of the cell extension function in the prior art. If there is a message to be transmitted, the handover request message may be included in the message and transmitted.

In step S560, the first base station determines whether the elapsed time since the cell extension area function is deactivated exceeds a preset time.

Here, the predetermined time may be the maximum time required for the second base station to hand over a terminal in which RLF may occur to the first base station, and the maximum time is determined by the number of terminals requiring handover. can be determined

If the elapsed time after deactivating the cell extension area function does not exceed the predetermined time in step S560, it can be seen that there are still terminals that need to be handed over from the second base station to the first base station, so the first base station determines the ABS function activation state. keep

On the other hand, if the elapsed time after deactivation of the cell extension function exceeds the predetermined time, it can be considered that the handover from the second base station to the first base station is completed. In this case, the first base station activates the ABS function through step S570. deactivate it

Therefore, according to the present invention, even if the deactivation of the cell extension function is detected, the first base station can prevent RLF that may occur in the terminal by maintaining the active state of the ABS function for a preset time, and after the preset time , By disabling the ABS function of the first base station, communication efficiency of the first base station can also be improved.

6 is a diagram illustrating a communication method of a first base station according to an embodiment of the present invention.

The communication method of the first base station illustrated in FIG. 6 is generally similar to the communication method of the first base station illustrated in FIG. 5 . However, in FIG. 6, when it is detected that the cell extension function is deactivated, the first base station does not maintain the ABS function activated for a preset time, but deactivates the ABS function until receiving a handover complete message from the second base station keep the state

Specifically, the first base station transmits a handover request message to the second base station through step S640. Subsequently, when the first base station receives a handover complete message from the second base station through step S650, the first base station deactivates the ABS function through step S660. (Steps S610 to S640 are described in FIG. 5. Since it has already been mentioned in the description, it will be omitted.)

That is, according to the communication method of the first base station shown in FIG. 6, since the first base station maintains the ABS function activation state until receiving the handover complete message from the second base station, the cell extension area function is deactivated. It is possible to prevent RLF generation of the terminal.

The handover complete message can also be received by the first base station from the second base station through a separate step only for receiving the handover complete message, or the first base station can receive the handover complete message from the second base station due to the inactivation of the cell extension area function. If there is a message received from , the handover complete message may be included in the message and received.

7 is a diagram illustrating a handover method of a second base station according to an embodiment of the present invention.

In step S710, the second base station may receive a handover request message generated due to the inactivation of the cell extension function from the first base station.

After that, in step S720, the second base station determines a terminal to be handed over to the first base station. More specifically, when the cell area of the second base station is changed from the first area to the second area due to inactivation of the cell extension area function, the second base station is positioned inside the first area and outside the second area. and determines a terminal connected to the second base station as a terminal to be handed over to the first base station.

After that, in step S730, the second base station hands over the terminal determined through step S720 to the first base station. Here, the UE may be a pico CRE UE (a UE located in a cell extension area of a pico cell and using the pico cell as a serving cell) as described above.

Then, when the second base station determines that the handover of all terminals located inside the first area and outside the second area is completed, the second base station generates a handover complete message in step S740.

Here, the handover completion message may include, in addition to information indicating that the handover of the terminal requiring handover has been completed, information on time required to complete the handover after receiving the handover request message and information on the handed over terminal. there is.

Thereafter, in step S740, the second base station transmits the generated handover complete message to the first base station.

Through the transmission of the handover complete message, the first base station deactivates the ABS function, and accordingly, the second base station whose cell area is changed to the second area communicates with a terminal located in the second area.

8 is a diagram illustrating a handover method in a wireless communication system supporting an eICIC function according to an embodiment of the present invention, in which a first base station is a macro base station 810 and a second base station is a pico base station 820. it is depicted

When the deactivation of the cell extension area function is detected through step S830, the macro base station 810 does not immediately deactivate the ABS function and maintains the ABS function activated state through step S835.

Thereafter, the macro base station 810 generates a handover request message in step S840, and the macro base station 810 transmits the handover request message to the pico base station 820 in step S845.

Upon receiving the handover request message, the pico base station 820 determines a terminal to be handed over to the macro base station 810 through step S850. Specifically, when the cell area of the pico base station 820 is changed from the first area to the second area due to inactivation of the cell extension area function, the pico base station 820 is located inside the first area and operates in the second area. A terminal located outside and connected to the second base station is determined as a terminal to be handed over.

Thereafter, the pico base station 820 hands over the terminal determined through step S850 to the macro base station 810 through step S855, and generates a handover complete message through step S860 when the handover is completed.

Here, the UE may be a pico CRE UE (a UE located in a cell extension area of a pico cell and using the pico cell as a serving cell) as described above.

Thereafter, the pico base station 820 transmits a handover complete message to the macro base station 810 through step S865, and upon receiving the handover complete message, the macro base station 810 deactivates the ABS function through step S870.

Through this, RLF may not be generated in the terminal located in the extended area of the pico base station 820 due to the inactivation of the cell extension function, and finally, the macro base station 810 deactivates the ABS function to communicate with the terminal. efficiency can be improved.

The time required from step S835 after the cell extension function is deactivated to step S870 when the ABS function is deactivated may be t, where t is required to hand over the terminal from the previously disclosed second base station to the first base station can be the maximum time.

9 is a block diagram illustrating the internal structure of a first base station according to an embodiment of the present invention.

In a heterogeneous network wireless communication system including a first base station 900 and a second base station supporting a cell range expansion (CRE) function, the first base station 900 determines whether or not the cell extension function is deactivated. A first base station controller 910 that monitors and detects inactivation of the cell extension function, and generates a handover request message, and a first base station transceiver that transmits the handover request message to the second base station ( 920) may be included.

The controller 910 of the first base station may maintain an almost blank subframe (ABS) function activation state of the first base station for a predetermined time when deactivation of the cell expansion region function is detected.

In addition, due to the inactivation of the cell extension function, the cell area of the second base station is changed from the first area to the second area, and the handover request message is located outside the second area and is located outside the first area. It may be a message requesting handover of a terminal located inside and connected to the second base station to the first base station.

Here, the UE may be a pico CRE UE (a UE located in a cell extension area of a pico cell and using the pico cell as a serving cell) as described above.

The first base station transceiver 920 may receive a handover completion message from the second base station, and the first base station controller 910 completes the handover through the first base station transceiver 910. When the message is received, an Almost Blank Subframe (ABS) function of the first base station 900 may be deactivated.

10 is a block diagram illustrating an internal structure of a second base station according to an embodiment of the present invention.

In a heterogeneous network wireless communication system including a first base station and a second base station 1000 supporting a Cell Range Expansion (CRE) function, the second base station 1000 operates by deactivating the cell extension region. A second base station transceiver 1020 for receiving the generated handover request message from the first base station and a second base station control unit for handing over at least one terminal determined based on the handover request message to the first base station ( 1010) may be included.

Due to the inactivation of the cell extension function, the cell area of the second base station 1000 is changed from the first area to the second area, and the second base station controller 1010 is located inside the first area and A terminal located outside the second area and connected to the second base station may be determined, and the determined terminal may be handed over to the first base station.

Here, the UE may be a pico CRE UE (a UE located in a cell extension area of a pico cell and using the pico cell as a serving cell) as described above.

The second base station control unit 1010 may generate a handover complete message after completing the handover of the terminal, and the second base station transceiver 1020 may transmit the handover complete message to the first base station. can

On the other hand, the embodiments of the present invention disclosed in the present specification and drawings are only presented as specific examples to easily explain the technical content of the present invention and help understanding of the present invention, and are not intended to limit the scope of the present invention. That is, it is obvious to those skilled in the art that other modifications based on the technical idea of the present invention can be implemented. In addition, each of the above embodiments can be operated in combination with each other as needed. For example, a base station and a terminal can be operated by combining parts of embodiments 1, 2, and 3 of the present invention. In addition, although the above embodiments have been presented based on the LTE system, other modifications based on the technical idea of the above embodiments may be implemented in other systems such as 5G or NR systems.

Claims (20)

A method performed by a first base station in a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function,
monitoring whether the cell area extension function is deactivated;
generating a handover request message when deactivation of the cell area extension function is detected; and
Transmitting the handover request message to the second base station;
Based on the inactivation of the cell area extension function, the coverage area of the second base station is changed from a first area to a second area;
The first area is an area extended compared to the second area,
The handover request message is used to perform handover from the second base station to the first base station to a terminal located in an area that is within the first area and not the second area,
method.
According to claim 1,
Further comprising maintaining an almost blank subframe (ABS) function activation state of the first base station for a predetermined time when deactivation of the cell area extension function is detected,
The predetermined time is a maximum time required for the second base station to handover the terminal to the first base station.
delete delete According to claim 1,
Receiving a handover complete message from the second base station; and
Deactivating an almost blank subframe (ABS) function of the first base station after receiving the handover complete message;
The first base station is a macro base station, and the second base station is a pico base station.
delete In a method performed by a second base station in a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function,
receiving a handover request message generated by deactivation of the cell area extension function from the first base station; and
Performing handover of the terminal determined based on the handover request message from the second base station to the first base station;
Based on the inactivation of the cell area extension function, the coverage area of the second base station is changed from a first area to a second area;
The first area is an area extended compared to the second area,
The terminal is located in an area within the first area and not the second area,
method.

delete According to claim 7,
generating a handover completion message after the handover of the terminal is completed; and
Transmitting the handover complete message to the first base station;
The first base station is a macro base station, and the second base station is a pico base station.
delete In the first base station of a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function,
a controller configured to monitor whether the cell area extension function is deactivated, and generate a handover request message when the cell area extension function is deactivated; and
A transceiver configured to transmit the handover request message to the second base station;
Based on the inactivation of the cell area extension function, the coverage area of the second base station is changed from a first area to a second area;
The first area is an area extended compared to the second area,
The handover request message is used to perform handover from the second base station to the first base station to a terminal located in an area that is within the first area and not the second area,
first base station.
According to claim 11,
The control unit is further configured to maintain an almost blank subframe (ABS) function activation state of the first base station for a predetermined time when deactivation of the cell area extension function is detected,
The preset time is the maximum time required for the second base station to handover the terminal to the first base station,
first base station.
delete delete According to claim 11,
The transceiver is further configured to receive a handover complete message from the second base station,
The controller is further configured to deactivate an almost blank subframe (ABS) function of the first base station when the handover complete message is received through the transceiver,
The first base station is a macro base station, and the second base station is a pico base station.
first base station.
delete In a second base station of a heterogeneous network wireless communication system including a first base station and a second base station supporting a cell range expansion (CRE) function,
a transceiver configured to receive a handover request message generated by deactivation of the cell area extension function from the first base station; and
And a control unit configured to perform handover of the terminal determined based on the handover request message from the second base station to the first base station,
Based on the inactivation of the cell area extension function, the coverage area of the second base station is changed from a first area to a second area;
The first area is an area extended compared to the second area,
The terminal is located in an area within the first area and not the second area,
Second base station.
delete According to claim 17,
The control unit is further configured to generate a handover completion message after completion of the handover of the terminal,
The transceiver is further configured to transmit the handover complete message to the first base station,
The first base station is a macro base station, and the second base station is a pico base station.
Second base station.

delete

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